1. Field of the Invention
This invention concerns a zoom lens used in a photographic camera, and in particular concerns a zoom lens comprising at least four lens groups wherein the focal length can be varied by moving these groups relative to one another.
2. Description of the Prior Art
A conventional zoom lens comprising four lens groups is disclosed in, e.g., Japanese Laid Open Publication No. Hei 1-178912, No. Sho 58-4113 and No. Sho 60-55313.
However, in this conventional four group zoom lens, an aperture disposed in the vicinity of the third lens group is displaced together with the third lens group, when the power (focal length) is varied. If the aperture is disposed near the third lens group, the diameter of the first lens group increases in comparison to when it is disposed near the object. The focal length tends to increase, and the first lens group has to be displaced by a greater amount for focusing. If this displacement is large, a large part of the marginal light in the maximum view angle is cut off by the frame of the first lens, when the first lens group is displaced towards the object. The amount of light in the peripheral region tends to decrease. To decrease the minimum photographic distance, thereof the diameter of the first lens group must be further increased. If its diameter is fixed, the minimum photographic distance is not short.